Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because, e.g., of its non-impact, low-noise characteristics, its use of plain paper and its avoidance of toner transfers and fixing ink jet printing mechanisms can be categorized as either continuous ink jet or drop on demand ink jet.
Continuous ink jet printing dates back to at least 1929. See U.S. Pat. No. 1,941,001 to Hansell. Conventional continuous inkjet utilizes electrostatic charging tunnels that are placed close to the point where the drops are formed in a stream. In this manner individual drops may be charged. The charged drops may be deflected downstream by the presence of deflector plates that have a large potential difference between them. A catcher (sometimes referred to as a "gutter") may be used to intercept either the charged or the uncharged drops, while the non-intercepted drops are free to strike a receiver or recording medium. U.S. Pat. No. 3,878,519, which issued to Eaton on Apr. 15, 1975, discloses a method and apparatus for synchronizing droplet formation in a liquid stream using electrostatic deflection by a charging tunnel and deflection plates. The function of a deflection charge plate and its associated catcher in a continuous jet printer is well known, being described in U.S. Pat. No. 4,107,699 which issued to Kenworthy on Aug. 15, 1977, The catcher may be an integral part of systems which serve multiple functions, including: blocking unwanted ink droplets, collecting and removing unwanted ink droplets, measuring drop charge levels, recycling ink, and solving start-up and shut-down problems.
Individual ink droplets receive an electrical charge. An opposite electrical charge is applied to the surface of a catcher parallel to the normal trajectory of the ink stream. The opposite polarities create an attraction force that deflects the droplets toward and onto the surface of the catcher. However, the disadvantage of this type of catcher is that when ink strikes the surface of the catcher the force of the drop impact causes the ink to splatter and/or mist. Ink splatter and mist creates unwanted artifacts on the printed media that reduces image quality and the splatter and mist contaminate other components in the printer.
U.S. Pat. No. 4,757,328, which issued to Braun et al. on Jul. 12, 1988, illustrates an assembly of a catcher that minimizes splattering and misting. However, this type of catcher affects print quality in other ways. The need to create an electric charge on the catcher surface complicates the construction of the catchers and it requires more components. This complicated catcher structure requires large spatial volumes between the print head and the media, increasing the ink drop trajectory distance. Increasing the distance of the drop trajectory decreases drop placement accuracy and affects the print image quality. There is a need to minimize the distance the drop must travel before striking the print media in order to insure high quality images.
Scanning type ink jet print heads, such as shown in the Braun et al. patent, experience acceleration forces that "fling" onto the media ink that has built up on the catcher. In order to minimize the amount of ink flung onto the media, a vacuum is commonly applied at one end of an ink removal channel to assist in removing the ink build up. However, air turbulence created by the vacuum decreases drop placement accuracy. Thus, paper dirt and debris is easily collected, causing the catcher to become clogged.
It can be seen that there is a need to provide a simply constructed catcher that reduces ink splattering and misting, increases fluid removal without affecting ink drop trajectory, and minimize clogging of the catcher due to exposure to environmental debris such as paper dust.